Hammer

Abstract

An electrically powered hammer is provided comprising a housing, a spindle, a hammering mechanism including a piston reciprocatingly mounted within the spindle, a wobble drive arrangement reciprocatingly connected to the piston, a trunnion arrangement including a cross bolt is driving engaged between the wobble drive arrangement and the piston, and wherein the piston includes a pair of piston arms and a protrusion so that the first piston arm and the protrusion define a first recess and the second piston arm and the protrusion define a second recess, and each of the recesses is shaped so as to support a wear reducing washer in an assembled position. When assembled each washer fits around the cross bolt in a region adjacent the inwardly facing face of the associated piston arm so as to reduce wear between the cross bolt and the piston arms.

1. A piston for a hammering mechanism of a powered hammer including a hollow spindle, a trunnion cross bolt, and at least one washer defining a central hole, the piston comprising:
 a cylindrically shaped piston body, slideably mountable within the hollow spindle, and including a rearward end; 
 at least one piston arm extending rearwardly from the rearward end of the piston body, the piston arm defining a through hole within which the trunnion cross bolt is mountable; 
 a protrusion located on the rearward end of the piston body, the piston arm and the protrusion defining a recess, the recess shaped to support the washer between the protrusion and the piston arm so that the central hole of the washer and the through hole of the piston arm are substantially aligned in preparation for the mounting of the trunnion cross bolt. 
 
     
     
       2. A piston according to  claim 1  wherein the protrusion includes an arcuate bearing surface. 
     
     
       3. A piston according to  claim 1  wherein the rearward end of the piston body includes an arcuate bearing surface between the piston arm and the protrusion, and the arcuate bearing surface is shaped to substantially conform to the washer. 
     
     
       4. A method of assembling a piston and trunnion arrangement sub-assembly of an electrically powered hammer comprising the steps of:
 providing a piston including a piston arm and a protrusion located on a rearward end of the piston, and defining a recess between the piston arm and the protrusion; and the piston arm defining a through hole; 
 providing a washer defining a bolt hole; 
 supporting the washer in the recess such that the bolt hole and the through hole are substantially aligned; and 
 mounting a trunnion cross bolt by passing the cross bolt through the washer bolt hole and the piston arm through hole.